Apparatus for determining a chemically reactive gas



Fafiay 22 1951 E; A. MCCLENDON 2,554,414

APPARATUS FOR DETERMINING A CHEMICALLY REACTIVE GAS Fiied July 12, 1945 2 Sheet s-Shet 1 Y y 22, 1951 MCCLEN DON 2,554,414

E. A. APPARATUS FOR DETERMINING A CHEMICALLY REACTIVE GAS Filed July l2,k 1945 2 Sheets-Sheet 2 24A 43A 95 44A 26A n 17 y H9 124 10s 126 El I09 INVENTOR E.A.MC CLENDON A'ITORNE Patented May 22, 1951 APPARATUS FOR DETERMNING A CHEM- ICALLY REACTIVE GAS Ernest A. McClendon, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application July 12, 1945, Serial No. 604,607

Claims.

This invention relates to a hydrogen sulfide recording apparatus. In one of its more specific aspects it relates to an automatic mechanism for continuously recording hydrogen sulfide concentrations in gaseous mixtures containing this gas.

Continuously operating devices for recording hydrogen sulfide concentrations in gaseous mixtures have been none too satisfactory. A test method of long standing involves the use of moist lead acetate paper, when if hydrogen sulfide is present, black to grayish lead sulfide will be precipitated on the white paper. This method, while satisfactory in a qualitative way, must be carried out by hand. Rate of blackening of the test paper or the intensity and extent of blackening are considered to indicate degree of concentration. That is, a moist test paper which when exposed to a gas containing hydrogen sulfide is immediately blackened is an indication of a high or relatively high concentration of this gas. Most chemists are familiar with the qualitative use of such test paper.

Commercial or pilot plants operating on a continuous scale may have need for continuous recordings of hydrogen sulfide concentrations at certain process points just like temperature and pressure records are now considered indispensable.

I have devised an apparatus for automatically and continuously making permanent records of hydrogen sulfide concentrations in gases.

One object of my invention, broadly, is to provide such an apparatus.

Another object of my invention is to provide an automatically operating quantitative hydroen sulfide recorder.

Still another object of my invention is to provide a continuous or substantially continuous recorder for hydrogen sulfide in gases which apparatus does not require the services of an operator.

These as well as additional objects and advantages will be apparent to those skilled in such art by reference to the following detailed description and annexed drawing which respectively describes and illustrates a preferred embodiment of the invention, and wherein Figure 1 represents a diagrammatic elevational view of one form of my apparatus.

Figure 2 represents a wiring diagram for use with my apparatus when a permanent record is not required.

Figure 3 represents a wiring diagram for use with my apparatus when a permanent record is required.

Referring to the drawing and particularly to Figure 1, a strip of porous, unglazed paper I I, about a half-inch in width is threaded from a roll I2 between three sets of rollers l3, l5 and It. Used paper is wound on a used paper roller l1. Between the two sets of rollers [55 and I5, the paper passes between a set of small rollers l4, one of which is partly immersed in a chemical solution contained in a vessel 3. This roll of paper is ultimately transferred from the original new roll I2 to the used paper roll ll during the operation of my apparatus. This entire paper transferring system is powered by a motor I9, through a speed reduction apparatus 2|. This speed reducer 2| is in direct connection with a rotatable shaft 22. On the opposite end of this shaft is a friction drive apparatus for rotating the used paper roll ll. Also mounted on this shaft is a bevel gear 23 which meshes with a bevel gear 24 on one of the wheels l6. The positive drive cannot be on wheel I? since its circumference increases as used paper accumulates thereon. The strip of paper also passes through a photoelectric apparatus 24, a gas exposure cell 25 and a second photoelectric apparatus 26. These mechanisms will be explained later in detail.

The chemical solution mentioned above as contained in vessel i8 is added to this vessel by way of a tube 2! and a source of stock solution contained in a stock vessel 28. An overflow tube 29 is inserted in vessel l8, as shown, in order to maintain a certain liquid level therein. A side arm from this overflow tube carries a funnel 3| to catch drippings from wheels l5 in case excess chemical solution is carried by the paper and removed by the rolls [5. It is obvious, however, that the funnel 3| need not be connected with the overflow tube 29, since a separate tube may be used, the main point being only a disposition of overflow solution from vessel l8 and droppings from wheels [5. I have combined these disposals merely as a matter of simplicity. A trap or siphon 29a seals off outside gases.

Any suitable means may be used for maintaining a substantially constant liquid level in container I8. I have used the particular method illustrated in Figure 1 because of simplicity and ease of construction. As shown, the position of the lower end of the tube 21 determines the liquid level. The lower limit of the level is determined by the point at which air is admitted into the tube thus permitting liquid to flow by gravity from reservoir bottle 28 through the tube 21 into container 18, the amount of liquid so added to container l8 being dependent upon the volume of air admitted. Thus as soon as the level rises sufficiently to cover the open end of tube 21 the fiow of liquid is stopped. The tube 29 is merely a safety device to prevent accidental over addition of liquid to the vessel 18, and is simply an overflow tube of appreciable diameter, so large in fact as to be able to carry away liquid as fast as it can run by gravity through tube 21 should the bottle 28. become accidentally broken and destroying the partial vacuum in its uppermost portion. For best protection the bottle 28 should be mounted at one side of vessel [8 and not directly over rollers l4 and-the paper strip at this point.

The motive power for driving the rollers la isfurnished by the drive shaft 22 and motor I9. I have shown rollers 66 as being the drive rollers, while friction of rollers !5, I4, I3 and I2 tend to maintain .some tension on the strip of paper, especially while passing through apparatus members 24, 25 and 26. In case construction of the apparatus is such that thepaper after being moistened with reagent in vessel 18 becomes weakened and subject to breakage between rollers i4 and spool ll, then the rollers l3 and I may well be equipped with bevel gear drives similar to that shown in connection with rollers l6. As mentioned hereinabove the used paper roller if is turned by a friction drive wheel 32, the friction drive being used since the circumference increases during the use of a roll of test paper.

Hydrocarbon or other gas to be tested forhydrogen sulfide from a source, not shown, by way of a sample line 33, passes through a pressure regulator and filter 34, through a manometer 35' and on into the gas exposure apparatus 25. The sample line 33 carries a hand operated, valve 30 located for manual operation. A small gas exhausting pump 38 powered by the motor I9 serves to remove gases from the gas exposure apparatus and such air as enters the exposure apparatus 25 through openings 36, by way of an exhaust pipe 31. From the exhausting pump 38 these gases are expelled from the apparatus through a discharge line 39 for such disposal as desired. The pressure regulator discharges the gas to be tested at a pressure only sufiiciently great to cause flow of such an amount as to permit satisfactory operation of the gas exposure member 25.

The gas exposure member 25 is composed of several portions, a gas exposed cell proper 4|, a hood member 42 covering the gas exposure cell ill, the hood member containing the slots 36. The lower and open end of the cell il terminates at a point just above the strip of paper II as the latter is threaded through the slots 36 of the hood member.

Briefly the operation of my apparatus is: the paper strip ii is. wetted with a doctor solution (aqueous sodium plumbite) by r-olls l4, one of which dips into this solution in vessel H3. The wetted'paper strip moves through the gas exposure cell 25. At the lower and open end of the gas exposure tube ll the gas such as a hydrocarbon gas containing hydrogen sulfide contacts the plumbite moistened paper. At this point, the paper turns dark with the precipitation of lead sulfide. The degree of this darkening or blackening is dependent upon several factors, among others, as concentration of hydrogen sulfide in the gas, length of exposure between the gas and a given section of the moistened paper, and the concentration of lead in the doctor solution. Thus, upon exposure in gas cell 25 a darkening of the paper occurs. This exposed section of paper is then moved to the photoelectric apparatus 26. This latter then operates photoelectrically to measure the intensity of a beam of light reflected by the lead sulfide darkened section of the paper. To offset or counteract adverse influences such as. color of paper or color or reflection.characteristic of the moistened paper, temperature, etc., a blank photoelectric apparatus 24 is used. This apparatus 2i uses a light source of the same intensity as that used in conjunction Withapparatus 26. Then by setting up subsequent apparatus, to be fully explained hereinafter, the differential in light refiection, that is, light reflected in apparatus 24 as opposed to that reflected in apparatus 26 is observed and/or recorded by a recording instrument. By previous calibration of the recording instrument in terms of grains of hydrogen sulfide per cubic foot or per cent by volume or by any other units desired, the hydrogen sulfide content of a gas may be observed and recorded as a permanent operating record.

In case an automatically made permanent record is not desired, the photoelectric assemblies may be of the photovoltaic type. In this type of instrument the exposure of the photocell to light causes an electromotive force to. be generated. Figure 2 of the drawing illustrates the electrical principles involved. in this embodiment. In. this figure, a photovoltaic apparatus 240.. corresponds to the photo unit 2 of Figure 1, While a second photovoltaic apparatus 260. corresponds to the photo unit 25 of Figure 1. The two units, 24a and 26a, are connected together so that the electromotive forces generated in each oppose each other. Inthis manner a, differential E. M. F. is available for measurement. This two-cell connection is then included in an electrical bridge type assembly, with some low resistances 18 and I9. A galvanometer 9a is connected between points and 95 as shown. On account of the very small E. M. F. differential which is generated by the opposed photovoltaic cells 24a and 26a, the galvanometer 24 should be of the high resistance type as to permit the flow of substantially no current. In this manner a more accurate voltage observation or in other words a more accurate galvanometer reading may be made. The galvanometer is of course equipped with a push button type switch. 91,. which may be constructed in the galvanometer, or an ordinary knife switch may be inserted in the circuit, as indicated by reference. numeral 16, orboth. The galvanometer readings or markings are then calibrated in terms of grains of hydrogen sulfide per cubic foot of gas or in terms of percentage by volume, or in any other terms desired. Then, an observation can be made merely by closing knife switch 16 and button switch 9'5 and noting the galvanometer reading and upon reference to a calibration chart, the corresponding concentration of hydrogen sulfide is found.

To, connect the electrical bridge of Figure 2 into the mechanism of Figure 1, it is merely necessary to connect wires 43a. and 44a of Figure 2 to wires 53 and M, respectively, of Figure 1. Then connect Wires 350; and 46a of Figure 2 to wires G5 and #6, respectively, of Figure 1. In this embodiment, then, cells t! and 4-8 of Figure 1 are the photovoltaic cells, which observe reflected light from the paper tape before and after exposureto hydrogen sulfide, respectively. For the photovoltaic cell assembly 24: is a source of light a9, a condensing lens 5|, a second condensing lens 5-25 and the actuallight'sensitive cell 41,

For the cell assembly 26 are the corresponding parts, a source of light 53, condensing lenses 54 and 55, and the light sensitive cell 48.

Some auxiliary equipment in connection with the photoelectric apparatus is a framing screen 56 and a lifting table 51 in the unit 24 and a framing screen 58 and a lifting table 59 with unit 26. These framing screens are merely flat black steel screens having a one-half inch square opening. The screens are so installed and arranged that the openings are directly over the paper strip. The steel lifting tables, flat black also, are arranged under the paper tape and directly under the framing screens. The purpose of these lifting tables is to 'raise the paper strip and hold it rigid against the underside of the framing screen at the time a photoelectric observation is made. The tables may be solenoid operated in a manner suitable for the purpose at hand. In fact from the raised observation position these lifting tables need to drop only such a distance as to permit free movement of the paper strip between the tables and the framing screen. Thus it will be obvious that inch or even less movement will be ample for this purpose. As shown in Figure l, the electric Wires 6| and 52 operate the solenoid of lifting table 51 while wires 63 and 64 lead electrical energy to the solenoid of lifting table 59. These solenoids are wired to operate simultaneously, that is, lead wires El and 52 are connected to one wire identified by numeral 55, while leads 62 and 64 are connected to a single wire 65. In this condition, then, when the operator closes a single switch blade identified by numeral II, then both solenoids operate to raise both lifting tables 51 and 59 simultaneously. A source of E. M. F. 12 is connected in a wire 13 which in turn may be connected directly to wire 65. Another wire 14 from the switch blade H connects with wire 55 to complete the solenoid circuits. Switch cross bar 15 is of an insulating material since blade H, blade 16 and blade 11 close independent and unrelated circuits.

The switch 88 carries a third blade 11 for closing a third electrical circuit. This blade of the switch closes a circuit from a source of current 93 through wires BI and 92 to wires 82, 83 am 84, 85. These latter wires are connected to wires BI and 92 in such a manner that closing switch blade 1'! illuminates both sources of light 49 and 53 simultaneously.

The electric motor l9 receives energy through lead wires Bi and 58 from a source of electrical energy 69. A switch 18, when closed, permits motor to operate thereby causing paper strip to unroll from roller l2, to pass between rollers l3, l4, l and I6 and to accumulate on the used paper roller I1.

This entire apparatus should preferably be enclosed in a case 8| as a means for protection. Gases and vapors in certain areas of petroleum refineries, gasoline plants and many chemical manufacturing plants contain hydrogen sulfide and such gas might have an adverse effect on the operation since lead sulfide darkening could occur on all exposed portions -of the paper strip which have been moistened with the treating solution by the rolls l4.

The fan or blower mechanism 38 is attached to the electric motor 19 to exhaust the atmosphere from within the case 8l. The gases and air enter the gas cell 25 by way of the slots 36 and pass through tube 31, through the blower and are discharged to the atmosphere through a the tube 39. To replace air so removed from within the case 8! an air inlet tube 68 conducts air from outside the case to the bottom of vessel 58 which contains some caustic soda solution or other solution adapted to remove hydrogen sulfide from air bubbling therethrough. In this manner only air free from hydrogen sulfide is permitted to enter the case 8|, which is otherwise substantially gas tight.

To prevent possible escape of hydrogen sulfide containing gas through slots 36 in the gas cell 25, it is preferable to close switch 18 and permit the motor l9 to operate the blower 38 continuously and at all times. Under these conditions then the paper tape would be in continuous movement resulting in waste of this strip paper. To prevent undue waste of paper, I have provided a gear disengaging mechanism 29 which operates in such a manner as to permit operation of motor I9 with or without rotation of shaft 22, as desired.

To operate the apparatus for the determination of the hydrogen sulfide content of a hydrocarbon gas, for example, I close switch 10 which starts the exhausting fan 38. I then engage speed reducing gear 2| by operation of mechanism 20 and the paper tape starts to move from roll IE to roll l1, and enroute becomes moistened with an alkaline plumbite solution by rolls [4, vessel [8 having previously been charged with such a solution. Valve 30 is then opened and gas to be tested flows through sample line 33, pressure regulator 34, manometer 35 into the gas exposure portion 4! of the cell 25. At the open end of tube 4| the gas comes in contact with a freshly moistened section of paper for a predetermined length of time. During this exposure the paper is darkened or blackened in proportion to the hydrogen sulfide content of the gas passing through tube 4!. After this exposure the exposed section of paper is moved to a position directly under the opening in the framing screen 58. At this time switch (shown in Figure 2) is closed which turns on sources of light 49 and 53, raises lifting tables 57! and 59 and closes the galvanometer circuit so that the needle of the galvanometer 94 will be deflected in proportion to the difference in intensities of the reflected light beams reaching the photovoltaic cells 41 and 48. 1f hydrogen sulfide is present in the gas, the reflected light absorbed by cell 48 'will be of less intensity than that absorbed by cell 41. With a galvanometer calibration chart having previously been prepared, then by reference to same, the concentration of hydrogen sulfide corresponding to the galvanometer deflection is found.

In the construction of this above explained embodiment of my invention, the photovoltaic cell assembly 25 should be located as closely to the gas cell 25 as mechanically possible. The exact location of the cell assembly 24 is of less consequence, but I prefer, also, to have this cell as close to the gas cell 25 as convenient.

This embodiment of apparatus may be operated in either of two manners, first intermittently, or second continuously. By intermittently, I mean the operation as explained above, that is, make an exposure on the paper tape while the latter is stationary, that, is not moving. Then, after exposure for a standard length of time, the gas may be shut off by closing valve 39 and the exposed portion of the paper tape moved to the framing screen 58 by manipulation of the gear disengaging mechanism 20. Then by closing ithe 53-b1ade :switch :80, :the photovoltaic cell: circuits are closed, the :liftingtables rise and theg'alvanometenneedle moves in proportion to thedifierentialtof.:light intensities reaching "cells 4I 'and 48.

In 'case :another determination :or a, check determinationisiidesired, tliisoperation may be repeated and as oft-en as desired.

The second or continuous method consists in running the tape from roll 'I 2 -to roll II atzall times, and with gas being tested flowing through the :exposurecell at all times. In this case :all tape x-from the exposure cell-25 to 'the right is colored or darkened according to the H28 content'of the :gas being tested. 'In this case a critical point is to make certain that any given ;-point on the'test paper remains under -.-the exposure tube M for a standard and predetermined length of time, such atime having been used in the calibration of the :mechanism. For example, a half minute "exposure time .may have been found necessary to .produce a'iproper darkening in intermittent determinations as hereinbefore explained, then if the opening of thegas exposure tube II is A,; inch by .%.-inch the length of time required for the --paper -to travel -inchashould bethissame minute. Any-desired rate of travel of-the papermay be accomplished through the gearreduction assembly -2 I:or by use of a variable speed motor I9.

.Af-ter sufficient time-ofoperation inthis manner thedarkening of thepaper is proportional to theHzS content of the-gas being-tested. In this case the =3- blade :switch 80 may be kept closed-at all times so that=a continuous=determination will be made. It is best :not to have the :galvanometer circuit closed during continuous operation :since galvanometers draw current :and the flow=of current tends to decrease "the voltage -generated. Itis-forthis reason that a galvanometer push button switch 91 is used. The ."pho-tocells and-allother-portions of the apparatus may be operating continuously and when a determination is to be made simply close the galvanometer circuit by push button 91. However, a certain time lag will be unavoidable, :and that time lag will be thelength of time required for a point on the paper tape .to "travel-from the exposure cell 4| to the framing screen'EB. .To shorten this time'lag is the-reason :for installing the framing screen 58at apoint as near-the 'gas cell 25 as-p'ossible. In actual construction the framing-screens :are placed verynear this gas cell since theplane of light travel from "the sources 4?) :and 53 to the :photocells '41 and 48 :may be at right angles to the line of travel of tthe paper tape 'in place of ;.-parali'el as shown in Figure -1. it is shown .in Figure .1 as beingparallelmerely 'to indicate therprinciple-of operation and tosillustrate more clearly the general mode-of :apparatus assembly.

By the use of the galvanometer M as explained hereinbefore no permanent record '01" the intermittent or continuous -H2S determinations is made. In most operations :such a permanent record :is desirable. :If the apparatus as above' explained "ismodified in a' c'ertainima-H- ner'a permanent'recordc'an be made by use'of a'standard'type of recorder.

:For use of a :potentiometer :for: recording :pur-

poses I -use a difi'erent kind of agphotoelec-tric cell, one known I as a iphctoemissivity T cell. This cell :is dependent u pon a change of electrical current :from: a :battery .or iother asource of con stant Z F. za's 'tocca'sionedlby: light of [varying intensity. Figure :3 represents ithe wiringdiagram for -useswith sairecording potentiometer Zinstrument sand either iphotoemiss'ivityior photoconductivity acells. :Either type of cell can be used with the wiring.diagram illustrated imFigure 3. fll're recorderiinstrumentrreferred to' by reference inumeral tIflI may be a :standard re cording potentiometer such as manufactured by a number zof Zinstrume'nt makers.

The .i-ph'otoemissivity -or .LDhOtOCOHdlICtiVitY cells I24 :and :IZG may .be connected "as :illustrated in Figure :3 :so that the net current flowingfrom the :pair of :cells will -representxthe differential *between the light absorbed by cells I24 and I26. This =electrical current differential orrrather'i'difierence .in iis amplified by aniamplifier tube "102 so :that a sufliciently =high l-M. E. will be available to operate -the recording .potentiometer 'I 0 I. :To .operate with such azdifi'erentialpf E. M. I suggestthense ofisuch a wiring :hookup as illustrated'in-Figure 3 which-is'a modified form of the well'knownGilbert circuit, but do not wish to limit my invention in any manner by this suggestion since other electrical hookups as obvious to those skilled in such-art ma'y *work equally as well. ln thi's-diagram.reference numeral 'Iii l refers to a battery :a source of constant current while resistances H13, I05 and I06 are inserted :in position :as rishown. Wire III connects thSiDGSitiVB iterminal of the battery I04 to theph'o'tocell I26. Wire 1115 conmeets the :plate of the-amplifier tube :102 with the wire III. The :grid =II-2 of the amplifier tube is 'connected by :a' wire I'El'I toa wire I08 which in turn connects the :two phot'oeells I25 and I24 as ishown. The other terminal of photocell I 24 is connected by a wire 109 to the other -terminal of -=the battery I04. -Wire II3 fromthe potentiometer goes -to a central iterminal'of the -battery-Ifl l while=wire- I-I'4 connects the potentiometer with anointbetween-resistances-I05and 1G6. Wire I'2il connects :wire I13 to resistance J06 which in turn connects to resistance .105 and theme on to the third terminal of the amplifier tube H32 sby way of a wire H0. The adjustable resistance *I 03' with wire -II-6 forms -a'=zero balance for the potentiometer, the wire tle connecting wire I09 with the variable resistance Ill-3.

To 'tie the circuit and :photocells =.of Figure 3 intothe-a-pparatus of Figure 1, wires 43 and 45 and photovoltaic cell 41 are removed from Figure '1 andcell J24 of-F igure 3 inserted-forthe cell 4W. Wires :IGB and I09 of Figure 3 of course remainconnected as shown. In a :similanmanner wires 44 and 46 and photovoltaic cell 48 of Figure 1 are removed and cell I26 .inserted in place of the iremoved-cell fl'a. Wires Jim-and III remain connected to the cell 126.

A three-blade switch 422 serves to open and close the photocell=circuits. Bar I23 'is-an insulating member to -=-hold rigid -the three blades of the switch -I22. .iBlade .I2l controls the recording potentiometer -:circuit as shown, blade I23'controls the source-10f-lightcircuit of Figure 1 since wire II! of Figure 3-:connects-wi-th wires '82 and-84 of Figure 1, and wire II8 of Figure 3 connects with wires --83 and-85=of:-Figure 1, the electrical :energy for lighting -light sources Hand 53 coming froma power source I35) :of Figure 3. =In .like manner the :switch blade "I29 controlstheoperation 'of the sole.-

noid lifting tables and 59 since wires H9 and I2! of Figure 3 connect with wires 65 and 66 of Figure l. A source of electrical energy l3l shown in line H9 of Figure l furnishes power for operating the solenoids.

Since this embodiment of Figure 3 is intended to operate continuously, it will be advisable to adjust the solenoid operated lifting tables 5? and 59 so that they will hold the paper tape ll firmly against the framing screens 56 and 58 but permit proper travel of the tape from the new roller 12 to the used roller ll. Other means for raising the lifting tables can be used, I merely suggest solenoids since they work well.

When the photocells I24 and 126 and wiring diagram shown in Figure 3 are substituted in the apparatus of Figure 1 as explained above, then a permanent record of the H28 content of a gas can be made.

To operate this combination I merely open valve 36 (of Figure 1) to permit sample gas to flow through the exposure cell 25, motor I9 operates to permit travel of paper tape through the apparatus as hereinbefore explained. The paper must travel sufiiciently slowly to permit a standard time exposure to H2S carrying gases in the gas cell 25. Of course, blower 38 continuously removes gases from the gas cell 25 and exhausts them through tube 39 as shown. When operating in this manner, a continuous record of HES concentrations in a gas can be made and I have found that my apparatus as herein described works very well when testing hydrocarbon and other gases.

As mentioned I do not wish to limit my invention by the particular galvanometer and potentiometer circuits given since they are merely exemplary, since other circuits known to those skilled in such art may work equally as well.

While my invention includes the use of two photovoltaic cells or two photoemissivity cells in their respective embodiments, I do not wish to limit my invention to the use of two cells, that is, one for measuring light reflection before exposure to HzS and one after. By assuming a definite light reflection from a strip of white pa per, I can operate my apparatus with only one photocell, that is, one installed to measure reflection of light from the tape containing the lead sulfide. With a proper calibration of either the galvanometer or the recording potentiometer reasonably accurate and dependable determinations can be made. I have found that for many purposes the accuracy of the one-cell apparatus is suflicient, but when accurate control of processing operations is necessary, the use of the two-cell apparatus is distinctly advantageous. One modification of apparatus which I have not shown on the drawing for reasons of simplicity is the use of a single source of light to furnish the incident light, that is, to replace the two light sources 49 and 53 of Figure 1.

Another modification which may be found useful under certain conditions is to measure the light of transmission passing through the tape Ii in place of measuring the reflected light as herein disclosed. Such a modification is useful when the sulfide formed is shiny and tends to reflect light in place of absorbing light.

I have mentioned above the use of a doctor or sodium plumbite solution for moistening the paper tape. I do not wish to limit my invention to the use of this lead containing solution for de-' termining the content of hydrocarbon gases Gil since the principle taught herein is of wide application and may be used for the quantitative determination of any compound in a gaseous mixture which compound forms another compound which absorbs light in such a manner that the absorption can be measured by light sensitive photoelectric cells.

For the determination of hydrogen sulfide l have found that a soluble lead salt in an alkaline solution, the regular doctor treating solutions for example, works exceptionally well. It works well when white light is used as the photoelectric light sources since the precipitated lead sulfide is quite black to white light and even very low concentrations of H28 produce a marked blackish or grayish coloration and these colorations are effective light absorbers. Other metal lic salts may be used for impregnating the paper, as for example, cupric compounds, mercuric compounds, nickel, cobalt, bismuth, cuprous and silver compounds which are sufliciently soluble as to form a solution sufficiently concentrated to impregnate the paper tape. The sulfides of these above mentioned metals are for the most part black and obviously are effective for absorbing white light. However, I have found that it is not necessary to use a metal ion which forms a black sulfide with H25 since such ions as arsenic, antimony or others which form colored sulfides may be used, since colored materials absorb light also.

In addition, it is not necessary that the sources of light emit white light since colored lights are also susceptible to absorption. For particular and specific problems one skilled in the art may select a certain colored light which gives an excellent absorption upon reflection by a sulfide of a certain color.

Further applications of my broad principle may be made when it is realized that other gases than hydrocarbons can contain materials other than hydrogen sulfide which give color reactions. For example, volatile acid in flue or other gases can be detected by using a paper tape moistened with an indicator solution which gives a color change with acid. Ammonia in gases can be detected in a similar manner.

The use of the sodium plumbite solution for moistening the paper may take a very black coloration with the hydrogen sulfide. A lead acetate solution or other soluble lead salts gives a black coloration, but none gave as black a color with a given concentration of hydrogen sulfide as does the alkaline sodium plumbite. This latter solution is inexpensive, works well, and is, in general, quite satisfactory.

Materials of construction of portions of my apparatus might well warrant a word of explanation. Most of the apparatus,however,may be constructed or assembled from standard equipment available on the market. Any parts coming in contact with the hydrogen sulfide containing gas or with the sodium plumbite solution should be resistant to corrosive action from these materials. The rollers It! should be constructed of materials which is resistant to corrosive action of the tape moistening solution, which in the preferred embodiment described herein is an alkaline sodium plumbite solution. I have found that sponge rubber rollers or rollers surfaced with sponge rubber serves well for wetting or moistening the paper tape. The rollers surfaces should be such as to moisten the paper uniformly so that black lead sulfide precipitate formed in the gas exposure cell may be uniform over the area Texposedito reflection by the framingiscreen: 58.-, If uniform, darkening; of. the paper. is notv accomplished thenresults; as.w measured. by;- the: photo cells cannot. be considered; dependable; The sponge. rubber rolls and surfaces which; I have used. gave uniform.- impregnation. of. the; paper tape.

Likewise rolls. l5 should be. resistant to doctor solution corrosion since theyassist-in removing excess, solutioncarried, by the paper: Rolls: [5 may. besomewhatlesssubject to,-corrosion than rolls .il5isince byv the timemoistened paper-reaches these, rolls a some: drying; may have; occurred. In any, event it, iswell to see. thatlthese rolls also areresistantrto possiblecorrosivezaction from-the moistenedipaperh When. either embodiment. ofmy invention: is used,' .that is,.the galvanometeror the-recording potentiometer instruments;cautiomshould-be exercisedto. make certain that. neither of these-instruments viseexposed. to corrosivepgaseousatmospheres. Eorrthis reasonitmig-ht bewell tomount them in aseparatercase.

Themain. housing: case .811! should have a-glass observation. window, and preferably theentire front; wall. mightwell be of g-lass-sfor observation purposes. Since the entireeassembly is not. large, Ihave foundlthatan all: glass: case 'held together by angleiron joints serves-well for the-purpose The lid-.for.thecaseshouldjbe removable; onpreferably the front observation glasslside-mig-ht be hingedfoneasy -accessu In any event, when closed for. operation,,the case .shouldibeareasonably: gastight since hydrogenl sulfide from an.- extraneous source, might prematurely, blacken' thezmoistened' tape as well as; form.v a black: precipitate. in-v the doctor, solutionsvessel. l 8.

I'have shown bottle 28 for containing; stock doctor. solution as. mounted within: the case. 8 l theapparat'usmay be constructed'in this man-. ner or. the. stock. solutions bottler may beset. outside the case,.as desired" The. electricimotorf l9 maybe .of; any standard type. on speedd'esired providing. suitable-gearreduction apparatuszl,beprovided.

The. paper. st'ocknsed with my: test apparatus mustbe such as to retaimacertain strengthwhen wetted with thesalkaline. plumbite solutiom.

Having. described my invention,. .I: claim 1;. An apparatus. for, measuring thecontent-ofza chemically reactive gas comprising; in'i combinatie a. first! roller, v.aflseoondr roller, driving means connected 'tosaid secondlroller, .saidrsecond roller beingv constructed. soras ,to :unwind: a: paper tape from said first roller to-saidrsecondroller: when r actuated by said driving means; and pass. said paper tape. through. means mounted intermediate said firstsandcsecondrrollerconsisting 0?, inorder,., an impregnatingcvessel; a-first photoelectridcelllassembly, a. gas exposure :cell, andiarsece ondlphotoelectriccell assembly; said gasrexposurecell being, further. characterized. in. that it: com prises. a; closed vertical. slotted hood, member, aa first. conduit.- extending through a. wallet. said hoodmember andlcentrally disposeditherein. with. its. inner. end' open andpositioned. adjacent jtoethe bottom. portioneofl said hood: member. and posi tioned above and betweensapair of, slotslocated in bottom portions ofcpposite walls ofv saidhood member, v said slotsl being. arranged. so: as to pass said panes. tape. horizontally therethrough, said first conduit. being adaptedtoconduct. a gaseous. mixture into. said.gas. cell, asecondconduit. at tached to said. hood; member. adapted. to exhaust and a1 recording potentiometer connectedito-said first andsecond photoelectric .cellassemblies;

2-; The apparatus; of. claim .1 wherein. the-g phostoelectric cell. assemblies; are ,photoem-issivity cell assemblies.

3. The apparatus: of claim: 1,, wherein the-photoelectric; cell assemblies: are: photoconductivity cell assemblies.

4. Thegapparatus of claim 1wherein themhotoelectric cellassemblies are photovoltaic" cellv assemblies.

5. Anrapparatus for measuringgthe-contentof a chemically reactive gas comprising in-.combina=- tion; agas-tight-vessel; including, a first roller; a

second roller, a motor connected to said second roller; said second: roller beinggconstrnctedrsoas to unwindapaper tape from: said; first rollers to said; second. roller;- when; actuated by said: motor andtpasssaidipaper tape throughmeansxmounted intermediate said first and seoondzroller-consistingof; in'order an..impregna-ting vessel, afirst photoelectric C8111 assembly; a gas exposure: cell, and a:secondphotoelectric:cell: assembly, saidgas exposure cellibeing furthercharacterized imthat it comprises a.. closed: vertical: slotted: hood" member;.afirst;: conduit!v extending througha wall of saidhood memberrandrcentrallw disposedtherein with: its. inner. end open and positioned adjacent to the. bottom-portion: of said L hood member and positionedlabove and between aepair-of-s slots- 10- cated-in-bottom aportionsmofopposite Walls :of. said ho od,.member3 saidzslots being arrangedsojasto pass said. paperL tape; horizontally -therethrough; saidfirst: conduit beingadapted to conduct; a

- gaseous mixture into said gasscelLaisecond conduit attached to said,hood.member andrextending outsidasaid g asetight; vessel av pump in:- said second conduit, a driving.connectionbetweemsaid pump and.saidimotor wherebysaid pump; and said conduit functionntoexhaustv gases -from'-with incsaid cell to.=the. atmospherepa-vessel adapted to contain as liquid. for absorbing, said. reactive gas a-..tubeflimmersed. saidrliquid and;v extending. outside said; gasrtightl vessel to, replace.- air withdrawn; through, saidslots, and: said; second conduit, the air thus:- replaceibeinge freed.v from reactive-gasby, bubbling throughssaidliquid, and a .recordmg-potentiometer connectedto vsaid first and secondphotoelectric. cells assemblies.

ERNESYIEA MCGLENDONN REFEREZICES The following references are. of record. in the. file. of this patent:

UNITED STATES.

Amen; Gas..Ana1ysis. and-misting of Gaseous Materials. (1955),. pages: 358.. and; 359,. quoting:

gases'from within i ell thg atmogphgre. 7:5 EederaLSpecificatiomof tan-tearlien-date. 

1. AN APPARATUS FOR MEASURING THE CONTENT OF A CHEMICALLY REACTIVE GAS COMPRISING, IN COMBINATION, A FIRST ROLLER, A SECOND ROLLER, DRIVING MEANS CONNECTED TO SAID SECOND ROLLER, SAID SECOND ROLLER BEING CONSTRUCTED SO AS TO UNWIND A PAPER TAPE FROM SAID FIRST ROLLER TO SAID SECOND ROLLER WHEN ACTUATED BY SAID DRIVING MEANS PASS SAID PAPER TAPE THROUGH MEANS MOUNTED INTERMEDIATE SAID FIRST AND SECOND ROLLER CONSISTING OF, IN ORDER, AN IMPREGNATING VESSEL, A FIRST PHOTOELECTRIC CELL ASSEMBLY, A GAS EXPOSURE CELL, AND A SECOND PHOTOELECTRIC CELL ASSEMBLY, SAID GAS EXPOSURE CELL BEING FURTHER CHARACTERIZED IN THAT IT COMPRISES A CLOSED VERTICAL SLOTTED HOOD MEMBER, A FIRST CONDUIT EXTENDING THROUGH A WALL OF SAID HOOD MEMBER AND CENTRALLY DISPOSED THEREIN WITH ITS INNER END OPEN AND POSITIONED ADJACENT TO THE BOTTOM PORTION OF SAID HOOD MEMBER AND POSITIONED ABOVE AND BETWEEN A PAIR OF SLOTS LOCATED IN BOTTOM PORTIONS OF OPPOSITE WALLS OF SAID HOOD MEMBER, SAID SLOTS BEING ARRANGED SO AS TO PASS SAID PAPER TAPE HORIZONTALLY THERETHROUGH, SAID FIRST CONDUIT BEING ADAPTED TO CONDUCT A GASEOUS MIXTURE INTO SAID GAS CELL, A SECOND CONDUIT ATTACHED TO SAID HOOD MEMBER ADAPTED TO EXHAUST GASES FROM WITHIN SAID CELL TO THE ATMOSPHERE AND A RECORDING POTENTIOMETER CONNECTED TO SAID FIRST AND SECOND PHOTOELECTRIC CELL ASSEMBLIES. 